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Through TEM observations it was established that PbO2 particles of the positive active mass are heterogeneous in mass distribution. Using electron micro‐micro‐diffraction it was found that PbO2 particles are built up of zones of α‐normaland/normalorβ‐PbO2 crystal structure with various orientation, and of amorphous zones. The latter are more transparent for the electron beam and are assumed to be hydrated. It was determined, through XPS (x‐ray photoelectron spectroscopy), that at least 30% of the PbO2 surface is hydrated. The changes in the crystal part of the active mass particles are followed during charge, discharge, open circuit, and overcharge. It was established that H2SO4 adsorption on the surface of the particles brings about an increase in their amorphous part. When the positive active mass is washed, its crystal part increases. It was also found that O2 causes amorphization of the particles, too. Oxygen atoms are sorbed by the PbO2 particles and increase their zones of disorder. A mechanism of formation of PbO2 particles during battery charge is proposed taking into account the processes of dehydration. OH− ions are assigned a considerable role in the interaction of the particles with the solution or with the neighboring particles.

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